The present invention relates generally to prosthetic devices arid, more particularly, to a component for facilitating rapid manufacturing of a prosthetic limb socket using fused deposition modeling or another similar multi-layer rapid fabrication technology.
A prosthesis is often used to replace an amputated portion of a limb and to help restore the amputee""s ability to use that limb. A prosthesis for a lower extremity amputation will often include an artificial foot connected to an upright assembly (pylon, tube or shaft) which is in turn connected to a custom fitted socket assembly. If the amputation is an above the knee amputation, the upright assembly will commonly include an artificial knee joint.
Such prosthetic devices typically include an outer socket made from a hard thermoplastic material. The outer sockets are conventionally created by heating a thermoplastic preform cone or a thermoplastic sheet, stretching the heated plastic over a positive mold of the socket (which is typically a modified positive cast of the amputee""s residual limb), and then vacuum forming the plastic in place over the positive mold.
In the field of prosthetics, the use and implementation of computer aided design and manufacturer (CAD/CAM) is becoming more and more prevalent, especially in the design and fabrication of the positive molds for the prosthetic limb sockets. See, for example, U.S. Pat. No. 5,824,111 to Schall. Presently, CAD/CAM systems are effective in digitizing an impression of the amputee""s residual limb, modifying the digital model using a CAD software design package, and then milling a positive mold of the socket on a computer numerically controlled (CNC) milling or carving machine based upon this modified digital model. Additionally, with the advent of such CAD/CAM systems, the use of modular endo-skeletal components, such as interconnection components for coupling the prosthetic limb socket to the upright assembly, is also becoming more and more prevalent. See, for example, U.S. Pat. No. 5,662,715.
U.S. Pat. No. 5,662,715 to Slemker discloses a modular interconnection component for a prosthetic limb assembly that resides within the distal end of the prosthetic limb socket. The component includes four holes bored into its distal end for receiving bolts extending from an attachment plate of an upright assembly into the distal end of the socket. Because the interconnection component and the attachment plate act to xe2x80x9csandwichxe2x80x9d the distal end wall of the socket, it is extremely important that this distal end wall be substantially flat and very strong. It is also important that the transition from the distal end walls to the side wall of the socket be substantially strong.
Another advancement currently being developed in the prosthetics field is the utilization of rapid prototyping technology in the fabrication of prosthetic limb socket. An example of such rapid prototyping technology is Fused Deposition Modeling (FDM), commercially available from Stratasys Inc. FDM is described in substantial detail in U.S. Pat. No. 5,121,329 to Crump. Generally, this process utilizes a CAD system for creating a digitized geometric model of an object. The three-dimensional dimensions of this object are then sent to a deposition apparatus which is designed to deposit multiple layers of a heated thermoplastic material (in a fluid state) onto a base so as to build a three dimensional version of the object as directed by the dimensions. Preferably, the material solidifies substantially instantaneously upon extrusion or dispensing onto the base, with the build up of multiple layers forming the desired object.
Therefore, rather than transmitting dimensions of a prosthetic limb socket mold to a CNC milling or carving machine to create a socket mold, the fabricator is able to transmit the dimensions of the finished socket to the FDM system, which will then create the finished socket in minutes. This general concept is also described in the Slemker greater than 715 patent.
One known difficulty in incorporating FDM in the fabrication of prosthetic limb sockets is the inability for FDM to provide substantially flat distal end walls of the socket as discussed above. Because the FDM system is designed to stack multiple layers of solidifying material on top of one another, a flat and strong horizontal surface is difficult to manufacture. For example, the system disclosed in the Crump patent extrudes heated plastic strands of material in a rectangular formation (longer sides are oriented on top and bottom) and the layer by layer overlap creates a bond between the layers. Accordingly, to provide the strongest structure, it is preferred that the layers are stacked upon one another. Therefore, it is difficult for this system to create a horizontal flat surface that is strong enough for use as a distal end of a prosthetic limb socket.
Accordingly, a need exists for facilitating the use of the rapid manufacturing systems in the manufacture of prosthetic limb sockets, which provides a substantially flat and extremely strong distal end surface of the prosthetic limb socket such that the modular interconnection components can be used.
The present invention facilitates the use of the rapid manufacturing systems in the manufacture of prosthetic limb sockets by providing a substantially flat and strong distal attachment plate or base for the deposition of the FDM materials thereon. The present invention also provides a method for fabricating a socket of a prosthetic limb which comprises the steps of: (a) providing a substantially flat distal attachment plate, where the attachment plate includes a coupling means carried thereon for coupling a prosthetic upright assembly thereto; and (b) repeatedly depositing layers of solidifying material to the proximal surface of the attachment plate, controlled, at least in part, according to the dimensions of the patient""s residual limb, so as to form a socket for receiving the patient""s residual limb. The attachment plate is preferably flat and rigid and includes a notch extending into the proximal surface and substantially about an outer periphery of the attachment plate so that, in step (b) above, at least one layer of the solidifying material is deposited into the notch so that the notch provides at least two faces for the first layer of solidifying material to bond to.
Accordingly, a prosthetic limb socket fabricated in such a manner will have a strong and substantially flat distal surface for coupling the endoskeletal prosthetic limb components thereto. Furthermore, the present invention facilitates the use of CAD systems and rapid manufacturing systems to fabricate prosthetic limb sockets in under an hour.
In one embodiment of the invention, the notch machined into the attachment plate is a helical notch, starting at a circumferential point at a first depth and ending at the circumferential point at a second depth, deeper than the first depth. Accordingly, the material deposited into the helical notch may build upon itself in a continuous helical layer.
Preferably, the attachment plate includes a plurality of bolt-receiving holes extending therethrough, and arranged in a standard four-hole pattern, for facilitating the coupling of a pyramid attachment plate to the distal surface of the socket.
Additionally, the rapid manufacturing system can be adapted to deposit two or more different types of material, at least one which hardens to be a substantially rigid material and another which hardens to be a material that is more flexible. Accordingly, the rapid manufacturing unit can be controlled to deposit the more rigid materials in portions of the socket that require greater support and strength and can deposit the less rigid and more flexible materials in portions of the socket that require less strength or that provide comfort to the patient""s residual limb.